Study on the Transformation Relationship of Three Waters and Water Cycle Mechanism of the Hailar River in the Hulunbuir High Plain from the Perspective of Multi-Method Coupling

To reveal the transformation laws of atmospheric precipitation, surface water, and groundwater under the dual drivers of climate change and human activities, this study takes the Hailar River in the Hulunbuir High Plain of Inner Mongolia as a typical research area, and constructs a multi—method coupling research framework of “isotope tracing —hydrodynamic verification—hydrochemical analysis.” Based on δD-δ18O isotope technology, the recharge sources of groundwater and surface water were identified; The transformation relationship between groundwater and surface water was further clarified by adopting hydrogeodynamic methods and groundwater chemical methods. Thus, the key processes and controlling factors of the transformation of the “three waters” in the inland high plain area were systematically clarified. The results show that: 1) atmospheric precipitation is the common recharge source of groundwater and surface water in the study area, which constitutes the core input path of the water cycle in the inland high plain; 2) The water residence time presents significant stratification characteristics: the residence cycle of surface water is generally shorter than that of groundwater; the residence time of groundwater prolongs with the increase of burial depth; and the renewal capacity of shallow groundwater is significantly better than that of deep groundwater; 3) there is obvious spatial heterogeneity in the recharge relationship of the “three waters” along the Hailar River: the upstream section is dominated by groundwater recharging river water, while the downstream section shifts to river water recharging groundwater, which reflects the dynamic response mechanism between the river and groundwater systems. This study clarifies the main controlling factors and spatial differentiation laws of the “three waters” transformation in the inland high plain area, and can provide a scientific basis and data support for the optimal allocation, rational development and utilization of regional water resources, as well as ecological protection.